The atmosphere of HD 209458b seen with ESPRESSO

We observed two transits of the iconic gas giant HD 209458b between 380 and 780 nm, using high-resolution ESPRESSO spectrograph. The derived planetary transmission spectrum exhibits features at all wavelengths where parent star shows strong absorption lines, for example, Na I , Mg Fe II Ca V H ? K . interpreted these as signature deformation stellar line profiles due to Rossiter-McLaughlin effect, combined with centre-to-limb effects on surface, which is in agreement similar reports recently presented literature. also searched species that might be present atmosphere but not spectra, such TiO VO, obtained a negative result. Thus, we find no evidence any absorption, including previously reported 209458b. high signal-to-noise ratio (~1700 590 nm) allows us compare modelled lines assuming different one-dimensional atmospheric models. conclude differences among various models observations remain within precision limits data. However, light curves are better explained when variation included computation only considered. This demonstrates currently best facility spatially resolving surface optical range transit carrying out empirical validations